1. Field of the Invention
The present invention relates to an optical ranging sensor for detecting a distance to an object and also relates to electronic equipment having the optical ranging sensor installed therein.
2. Description of the Related Art
As optical ranging sensors for detecting a distance to an object, conventionally, there have been an optical displacement measuring device (JP 2002-195807 A: Patent Literature 1) and an optical displacement gauge (JP 2006-38571 A: Patent Literature 2) in which light radiated from a light emitting element such as a laser diode is condensed by a light projecting lens, and a resultant beam is projected on an object to be measured, and then a portion of diffuse reflectance light, reflected by a surface of the object to be measured, is condensed by a light receiving lens so as to form a received light spot on a light receiving surface of an MOS (metal oxide semiconductor) image sensor, and finally the distance to the object to be measured is detected on basis of the position of the received light spot on the light receiving surface.
FIG. 11 shows a schematic configuration of the optical displacement measuring device disclosed in Patent Literature 1 and the optical displacement gauge disclosed in Patent Literature 2. As shown in FIG. 11, a CMOS (complementary metal oxide semiconductor) image sensor 1 as a light receiving element is not flush with a laser diode 2 as the light emitting element, and packages of the CMOS image sensor 1 and the laser diode 2 are separately formed. A signal processing unit 3 for processing signals outputted from the CMOS image sensor 1 and a driving circuit unit (not shown) for the laser diode 2 are formed outside a chip of the CMOS image sensor 1, and the CMOS image sensor 1, the signal processing unit 3, and the driving circuit unit are not provided in one chip.
FIG. 12 shows a plan view of the CMOS image sensor 1. A size of an effective light receiving part 1a in the CMOS image sensor 1 is required to be set in consideration of various variations in size, position and the like of a light spot 4 formed on the effective light receiving part 1a so that the position of the light spot 4 is within the effective light receiving part 1a even if the position varies. This point, however, is described neither in Patent Literature 1 nor in Patent Literature 2. The size of the effective light receiving part 1a is presumed to be considerably large from a moving range of the light spot 4 that moves with movement of the object to be measured and the size of the light spot 4.
The conventional optical displacement measuring device disclosed in Patent Literature 1 and the conventional optical displacement gauge disclosed in Patent Literature 2 have problems as follows.
The CMOS image sensor 1 is used as the light receiving element in such a conventional optical ranging sensor as described above. The effective light receiving part 1a of the CMOS image sensor 1, however, is not flush with the laser diode 2 as the light emitting element and the packages of the CMOS image sensor 1 and the laser diode 2 are separately formed, so that the CMOS image sensor 1, the signal processing unit 3, and the driving circuit unit are not provided in one chip. Accordingly, such an optical ranging sensor, which necessarily has a great overall size, causes problems of a large number of production processes, complexity of works in each process requiring accuracy, and increase in manufacturing cost.
Also, without any description about the size of the effective light receiving part 1a in the CMOS image sensor 1 therein, the size of the effective light receiving part 1a is presumed to be considerably large from the moving range of the light spot 4 that moves with movement of the object to be measured and the size of the light spot 4. Accordingly, a problem is caused in that the CMOS image sensor 1 involves a great chip size and hence great cost.
For determination of a center of gravity of the light spot 4 on the effective light receiving part 1a, as for characteristics, data from an unnecessary portion of the light receiving unit is captured and calculated because of the great size of the effective light receiving part 1a. This causes a problem in that increased time required for the calculation brings about increase in response time of the optical ranging sensor and increase in power consumption therein. Besides, the data from the unnecessary portion of the light receiving unit makes a noise in the determination of the center of gravity of the light spot 4, which noise results in decrease in S/N and increase in an error of a value of the determined center of gravity. As a result, there is caused a problem of deterioration in performance of the optical ranging sensor.